Improving the hydrological analysis of groundwater flow paths by integrating geochemical and physical characteristics of a highly fractured aquifer system to create sustainable use of groundwater in a climate with projected drying trends. Precipitation over Caribbean islands has decreased steadily since the 1950's, which has led to severe drought conditions. The most recent Pan-Caribbean Drought occurred from 2013 to 2016. Climate models predict that drying trends are expected to continue and become more severe over time as precipitation decreases and temperatures rise. In addition, evaporation rates on these islands are expected to increase by ~15-17%, contributing to the drought. Though fractured bedrock aquifers account for 20% of the world's aquifer systems, essential questions of how to characterize and quantify the magnitude of this type of subsurface storage in the context of water supply development remain poorly understood. This study aims to understand the magnitude of groundwater storage and water supply sustainability of one such aquifer system on the island of Tobago. This island is predominately composed of highly fractured Mesozoic igneous and metamorphic rocks with a well-developed saprolite soil cover. The vast majority of hydrogeologic research on small islands has been conducted on volcanic islands, which has produced valuable information about subsurface layer heterogeneity and its effect on flow rates and solute transport. However, there is limited information on groundwater behavior in geologically and structurally complex islands that are predominantly composed of fractured coarsegrain igneous crystalline rocks, as seen in Tobago. vii Here we present the results of this research, which shows inter-basin flow due to the connectivity of fractures and faults. Environmental tracers indicate that older groundwater (30+ years) is located in the island's southern region. This transport has supported multiple types of groundwater mixing trends. Finally, the quantification of recharge using climate models and 3- dimensional groundwater modeling shows the consistant reduction of storage in this aquifer to the year 2099.